Fluidising and feeding of finely divided materials



FLUIDISING AND FEEDING OF FINELY DIVIDED MATERIALS Filed Sept. 22, 19602 Sheets-Sheet l VACUUM PUMPR 38 COMPRESSOR V as r35 1 W I if 1 I 374 si/l. I 1 z 2 INVENTOR. ALLA/v MACKENZIE Dosuz June 11, 1963 A. M. DOBLE3,

FLUIDISING AND FEEDING OF FINELY DIVIDED MATERIALS Filed Sept. 22, 19602 Sheets-Sheet 2 INVENTOR. ALLA/v MACKENZIE 00515 nited States Patent3,093,418 FLUIDISING AND FEEDING F FINELY DIVIDED MATERIALS Allan M.Doble, 206 Poath Road, Melbourne, Victoria, Australia Filed Sept. 22,1960, Ser. No. 57,792 2 Claims. (Cl. 302-17) This invention relates tothe fluidizing and feeding of powdered, finely-ground and other finelydivided materials and refers especially, but is not limited to, thefeeding of abrasive material to blast guns and the like.

In the abrasive blasting art a system was proposed for fluidizing andfeeding finely-divided abrasive material from a closed container havingahorizontal porous bottom which provided for the entry of atmospheric airto fluidize the material when the interior of the container wasconnected to a vacuum pump or the like. This system employed a verticaldischarge pipe extending upwardly through the porous bottom into thebody of abrasive material in the chamber an'd this pipe, open at itsupper end, was connected at its lower end to an intermediate portion ofan air pipe which extends from the upper end of the closed container toa blast gun. The gun was arranged Within a sealed cabinet having ahopper bottom connected to the vacuum pump through a cyclone separator.The solid material consisting of the abrasive material and of particlesremoved from the workpieces within the cabinet, was returned from thecyclone to the container for re-circulation.

Thus, in the above described apparatus when the vacuum pump wasoperating and the valve of the gun was open, air was continuouslywithdrawn from the top of the sealed container and replaced by air whichentered through the porous bottom of the latter and which passedupwardly through and so fluidized the abrasive material therein. Also,the fluidized material continuously entered the upper end of thevertical discharge pipe and gravitated therefrom into the air pipe,whereby it was conveyed by the air stream to the blast gun.

In all such abrasiveblasting operations, the debris removed from theworkpieces, and which consequently becomes miXed wtih the abrasive, isgenerally of comparatively coarse particle size and thus it isundesirable that this material should be re-circulated. For this reason,in the aforesaid prior art system, the discharge pipe had its upper endlocated some distance above the bottom of the container, whereby whenthe bed was fluidized, it was intended that the coarser particlesgravitate to the bottom of the container where they could not enter thedischarge pipe.

However, the aforesaid system proved to have several disadvantages, oneproblem being that the coarse abrasive material or debris was notseparated to the desired extent within the closed container. Thus,during the operation of the apparatus a large number of the coarseabrasive particles and debris entered the vertical discharge pipe andwere re-circulated to the blast gun, and this seriously reduced thequality of the surface treatment in these fine particle abrasivesystems.

Another disadvantage of the prior art devices of the aforementioned typewas that they did not provide an effective means to regulate the rate offeed of the abrasive material. Such feed regulation is essential inorder to provide an efficient blasting operation under variousconditions including the type of material being treated and the surfacefinish desired.

Therefore, one principal objective of the present invention is toprovide na improved fluidizing and feeding apparatus for finely dividedmaterials which completely separates out the coarse abrasive particlesand debris and re-circulates only the fine particles to the blastinggun.

. 3,093,418 Patented June 11, 1963 -or alternatively, by connecting theinterior thereof to a source of reduced pressure.

Another important object of my invention is to provide a novelarrangement of components wherein a simple yet reliable means can beutilized to regulate the rate of feed of the abrasive particles in theair stream.

In carrying out the aforementioned objects, my invention includesapparatus comprising a storage chamber having a porous bottom, and anovel upstanding partition therein separating the storage chamber toform a feed chamber that is closed at its upper end and open at itslower end. The lower edge of the partition is spaced above the bottom ofthe storage chamber so that the coarse abrasive particles and debris maygravitate there- -below. .A discharge passage communicates with an upperportion of the feed chamber and restricted air passage connecting thestorage chamber above the material therein to an upper part of the feedchamber.

' Thus, when air or other gas enters the storage chamber, it passesupwardly through the porous partition and fluidizes the abrasivematerial, and some of the air then the highest within the feed chamberand an effective separation of coarse particles is thereby obtained.When the upper surface of this colurnn is disposed sufiiciently close tothe entrance to the discharge passage, the fiuidized material is thenswept thereinto by an air stream which flows substantially across thetop of the column. "The problem of regulating the rate of feed of theabrasive material has been solved in my invention by varyirig' theposition of the upper end of the column relatively to the dischargeopening and thisis preferably effected by means of a valve forregulating the flow of air through the restricted passage.Alternatively, provision may be made whereby the said discharge opening'may be raised or lowered to regulate the flow of abrasive p t c e v vAccording to a preferred arrangement of the present invention, the novelfeed chamber is formed by a more or less vertical duct which is arrangedcentrally within the storage compartment. The vertical duct ispreferably of a tapered formation so that it converges upwardly wherebythe velocity of the material increases as it rises up the duct. i 1

Other objects and advantages of the invention will appear from thefollowing description of a preferred embodiment and description of theoperation thereof, given in accordance with 35 USC 112.

In the following description of preferred forms of the inventionreference is made to the accompanying drawings wherein:

FIG. 1 is a view in elevation and in section showing apparatus accordingto one form of the invention;

FIG. 2 is a view in cross section taken along the line .22 of FIG. 1;and

FIG. 3 is a view in elevation and in section of apparatus according to amodified form of the invention.

The apparatus illustrated in FIGS. 1 and 2 of the drawings is directedto one form of my invention for fluidizing and feeding finely dividedabrasive particles. As shown, the apparatus 10 comprises a storagechamber 11 having an upper part of elongated vertical cylindrical formand a lower part of downwardly convergent conical shape. Attached to thelower end of the storage chamber 11 is an integral flange 12 of annularformation. Near the bottom of the storage chamber 11 are fixeddiametrically opposite lugs 13 which carry bolts 14 that are pivotallyconnected thereto. The bolts 14 carry wingnuts 15 and serve to retain inposition a filter box 16.

The filter box 16 comprises a plate 17 which is slotted to receive thebolts 14, and a ring 18 fixed to the plate 17 so as to define a circularspace within the filter box. The ring 18 has a flange 19 adapted toengage the flange 12 with a gasket 20 interposed. A spacing ring 21 isinserted within the filter box, and a disc 22 of porous stone or someother suitable porous material such as a resin bonded quartz filter, issupported by the ring 21 so that its upper surface is flush with theupper surface of the flange 19. An inlet pipe 23 is provided to admitair into the filter box below the porous disc 22. It will be evidentthat the filter box 16 is readily detachable to unload the storagechamber 11 and provide access thereto. If desired, an opening (notshown) may be provided in the side of the chamber 11 immediately abovethe filter 22, and provided with closure means which can be removed topermit the periodic removal of coarse particles which tend to settle onthe porous disc 22.

To perform the novel columnating action the fluidized abrasive particleswithin the storage chamber 11, I utilize a novel vertical duct or feedchamber 25 which constitutes an important feature of the invention. Thefeed chamber 25, as shown in FIG. 2, is preferably a rectangular shapein cross section and is arranged centrally within the chamber 11 withits upper end disposed above the normal level of the abrasive materialwithin the chamber 11, while its lower end is disposed a substantialdistance above the top of the porous disc 22. The duct 25 is closed atits upper end, while its lower end is open so as to communicate freelywith the interior of the chamber 11.

A discharge pipe 26 is arranged above the level of the material in thestorage chamber 11, and it extends through one wall of the feed chamber25 through the storage chamber 11 and out one wall thereof. An air inlethole 27 is formed in the wall of the feed chamber 25 at approximatelythe same height as the discharge pipe 26 so as to connect the feedchamber 25 to the upper portion of the storage chamber 11. A needle-typeregulator valve 28 extends through the wall of the storage chamber 11 soas to provide for regulation of the effective size of the air hole 27 byturning the handle 29 thereof. Thus the flow of air through the hole 27may be restricted to any desired extent.

As indicated in the drawings, the duct 25 is of oblong shape in planview as shown in FIG. 2; and the discharge pipe 26 extends centrallyinto one of the end walls thereof, while the air hole 27 is arranged inone of the side walls adjacent to the opposite end wall and on theopposite side of a shallow transverse baffie 30 which depends from theclosed upper end 31 of the duct and has its lower edge arranged slightlybelow the level of the discharge pipe 26. Thus the air must pass belowthe baflie 30 in flowing from the air inlet hole 27 to the dischargepipe 26.

The apparatus 10 illustrated in FIGS. 1 and 2 would normally be used forsupplying powdered abrasive material to a blast gun in a system similarto the type described above. Thus, to illustrate my invention as itwould be employed in a complete blasting system, I have shown thestorage chamber 11 arranged below a cyclone separator 32 or otherequivalent means, from which the abrasive and other solid materialdescends into the storage chamber 11. A vacuum pump 33 is connected tothe cyclone separator 32 by a duct 34. A blast gun 35 of theconventional ejector type wherein a high velocity compressed air jetinduces a secondary flow of abrasive-laden air is located within a blastgun cabinet 37 which is connected by a suction line 38 to the cycloneseparator 32. Accordingly, the blast gun 35 is connected to thedischarge pipe 26 and to a source of compressed air controlled by avalve '36. The air inlet pipe 23 is preferably connected to a silica-gelmoisture trap 39 to dry the air entering the storage chamber 11.

In the operation of the apparatus 10 when used in the abrasive blastingsystem shown in FIGS. 1 and 2, a partial vacuum is maintained in theblast gun cabinet 37 by means of the suction pump 33 connected to theblast gun cabinet 37 through the cyclone separator 32 located above thestorage hopper 11. When the valve of the blast gun 35 is open, air isinduced to flow into the cabinet 37 from the discharge pipe 26 throughthe gun 35. Thus the pressure in the feed chamber 25 is reduced to causea flow of air thereinto from the upper part of the surrounding storagechamber 11, but due to the restriction of the air hole 27, there is anappreciable pressure drop from the storage chamber 11 to the feedchamber 25.

The reduction in the air pressure due to the vacuum pump 33 within thestorage chamber 11 causes air to pass into the bottom thereof throughthe inlet pipe 23 and the porous disc 22 and then upwardly through theabrasive material which is thereby fluidized in the usual way.

Due to the reduced pressure within the feed chamber 25 and to thefluidized condition of the abrasive material, this material now riseswithin the chamber 25 in the form of a column as portrayed in FIG. 1 andwhen the surface of this column reaches a suflicient height, the air inflow ing across the chamber 25 and around the bafile 30 from theaperture 27 to the discharge pipe 26, sweeps over and erodes the surfaceof the column, so that the abrasive material is carried at acorresponding rate into the pipe 26. The position of the upper surfaceof the column may be varied, by controlling the pressure within theupper end of the feed chamber 25 by means of the regulating needle valve28, and thus the rate of feed of the material may be regulated asdesired.

As the lighter and smaller particles tend to rise higher than theheavier and coarser particles, a classifying action takes place. That isto say, the coarser particles do not rise to the top of the column, sothat an effective separation is produced. Thus the coarse particles tendto sink to the bottom of the storage chamber 11 and accumulate on thetop of the filter box 16 in the form of a layer as indicated in FIG. 1.This layer assists in uniformly distributing the incoming air in thebody of the finely divided material. However, if the amount ofaccumulated coarse material becomes excessive, it may be removedmanually through the opening referred to above.

Reference is now made to FIG. 3 of the drawings which illustrates,partly in schematic fashion, abrasive blasting apparatus includingfluidizing and feeding means according to another form of the invention.The apparatus shown in FIG. 3 comprises a sand blasting cabinet 40 tothe bottom of which there is connected a conical storage chamber 41. Atthe bottom of the storage chamber 41 a filter box 42 is mounted with aporous block 43 of the type previously described located therein.

The storage chamber 41 is provided with a central feed chamber 44, butinstead of being of uniform cross section the feed chamber 44 is made ofconical or pyramidal form so that its cross section diminishes towardsthe top. The upper end of the feed duct or chamber 44 is connected to adischarge pipe 45 which may extend outwardly through the wall of thechamber 41 or may be connected directly to a sand blasting gun 46 asshown in FIG. 3. The junction of the feed chamber 44 with the outletpipe 45 is effected by means of a T-joint 47, and a pivot tube 48 ismounted within the T-joint 47 so that it faces towards the outlet pipe45. A pipe 49 provided with a control valve 50 leads from the interiorof the cabinet 40 and is connected to the other arm of the T-piece 47.The valve 50 operates in a similar manner to the needle valve 28 shownin FIGS. 1 and 2, i.e. it serves to control the pressure differentialbetween the chamber 41 and the top of the feed duct '44 and so controlsthe height of the column of fluidized material in the feed duct 44.

The apparatus also includes a pressure air-line 51 having one branch 52which is connected to the filter box 4 2 through a valve 53, and asecond branch 54 which is connected to the blast gun 46 through a valve55.

In the operation of this form of the invention, compressed air suppliedby a compressor 57' and admitted through the valve 53 to the filter box42 causes the material within the chamber 44 to be fluidized, while thecompressed air admitted through the valve 55 to the blast gun 46 inducesa flow of air and suspended material through the outlet pipe 45 to theblast gun 46. The blasting gun 46 may be manipulated manually within thecabinet 40 using a flexible protective shield 58 in the wellknownmanner.

By closing the valve 50 to restrict the fiow through the pipe 49 and byopening valve 53 to increase the flow of fluidizing air, the amount ofabrasive particles carried through the pipe 45 can be increased, whereasif the valves 50 and 53 are operated in the reverse manner the amount ofabrasive particles in the air carried through the pipe 45 can bereduced.

An important feature of the construction of FIG. 3 is that at the bottomof the duct 44 the vertical travel of the abrasive particles iscomparatively slow whereas at the top of this duct the speed of travelof the particles is considerably greater in view of the smaller crosssectional area. It is found in practice that this arrangement leads toan even rate of feeding at both high and low concentrations of theabrasive particles in the air stream.

To those skilled in the art to which this invention relates, manychanges in construction and widely differing embodiments andapplications of the invention will suggest themselves without departingfrom the spirit and scope of the invention. The disclosures and thedescription herein are purely illustrative and are not intended to be inany sense limiting.

I claim:

1. Apparatus for fluidizing and feeding finely divided materialscomprising: a storage chamber having a porous bottom; a feed chambermounted within said storage chamber, said feed chamber comprising avertically ex tending duct open at its lower end and closed at its upperend, said duct having a frusto-conical form with a cross section thatdiminishes towards its upper end; the lower edge of said duct beingspaced above the bottom of said storage chamber whereby the material maygravitate therebelow; a restricted air passage connecting the storagechamber above the material therein to an upper part of said feedchamber; and a discharge passage communicating with an upper portion ofsaid feed chamber.

2. Apparatus for fiuidizing and feeding finely divided materialscomprising: a storage chamber having a porous bottom; a feed chambermounted within said storage chamber, said feed chamber comprising avertically extending duct open at its lower end and closed at its upperend, said duct having a cross section that diminishes towards its upperend and a lower edge spaced above the bottom or" said storage chamberwhereby the material may gravitate therebelow; a T-joint conduit havinga stem and two branches, said stern being connected to the upper end ofsaid duct; a pipe having a restricted air passage connecting the storagechamber above the material therein to one said branch of the T-joint;and a discharge conduit connected to the other said branch and therebyalso communicating with an upper portion of said feed chamber.

References Cited in the file of this patent UNITED STATES PATENTS2,707,132 Baresch Apr. 26, 1955 2,758,564 Randall Aug. 14, 19562,924,489 Beckmann Feb. 9, 1960

1. APPARATUS FOR FLUIDIZING AND FEEDING FINELY DIVIDED MATERIALSCOMPRISING: A STORAGE CHAMBER HAVING A POROUS BOTTOM; A FEED CHAMBERMOUNTED WITHIN SAID STORAGE CHAMBER, SAID FEED CHAMBER COMPRISING AVERTICALLY EXTENDING DUCT OPEN AT ITS LOWER END AND CLOSED AT ITS UPPEREND, SAID DUCT HAVING A FRUSTO-CONICAL FORM WITH A CROSS SECTION THATDIMINISHES TOWARDS ITS UPPER END; THE LOWER EDGE OF SAID DUCT BEINGSPACED ABOVE THE BOTTOM OF SAID STORAGE CHAMBER WHEREBY THE MATERIAL MAYGRAVITATE THEREBELOW; A RESTRICTED AIR PASSAGE CONNECTING THE STORAGECHAMBER ABOVE THE MATERIAL THEREIN TO AN UPPER PART OF SAID FEEDCHAMBER; AND A DISCHARGE PASSAGE COMMUNICATING WITH AN UPPER PORTION OFSAID FEED CHAMBER.